Nowadays smart energy management plays an important role in industrial indoor plant cultivations. Conventional light-systems and light programs, which are commonly used in greenhouses are not optimized for plant growth. Such artificial light systems have fixed light intensity and spectral composition of light. Moreover, over 80% of the spectral energy produced by such lamps is useless for photosynthesis, for induction of defence mechanisms and consequent growth, therefore this energy is wasted. One major difference between sunlight and artificial indoor plants cultivation-system is flexible light intensity and quality (spectral composition) that usually operate in the nature. In natural conditions plants are exposed to daily and seasonally variable light intensity and light spectral composition and sometimes to the ozone stress. Moreover indoor cultivated plants are never exposed to moderate ozone as found in natural conditions. It is also well known that indoor cultivated plants have lower nutritional, flavour and taste values for the consumers than plants cultivated outdoors.
Microorganisms, especially bacteria cause the most widespread plant diseases. These pathogens are able to survive and cause diseases under a wide range of environmental conditions. They are origins of major damage to economically important plants, sources of seedling blight (high mortality of seedlings), stem rot, leaf blotch etc. The present invention therefore is focused on the resolving the problem: how to grow plants (in greenhouse conditions) able to cope with pathogen infection in sustainable and low input agriculture systems and not to reduce their grow or yield. The invention will lead to use of the natural components of active plant defense (specific resistance capabilities) trigged by wavelengths of light of certain wavelength and the components of the cross-tolerance in which exposure to light can burst innate immunity. Thus both producers and consumers will benefit from invention, because novel methods of plant protection could result in lowering usage of chemicals (pesticides, fungicides and other) thus will protect environment and their application will have impact on human health.
It is known that the application of light from the UV spectrum (wavelengths shorter than visible light) is a highly effective method of destroying microorganisms. At certain wavelengths UV is mutagenic to bacteria, viruses and other micro-organisms e.g. at a wavelength of 254 nm [4] UV will break the molecular bonds within micro-organismal DNA, producing thymine dimers in their DNA thereby destroying them, rendering them harmless or prohibiting growth and reproduction. However, UV-B and UV-C is problematic to handle for humans and is heavily implicated in cancerous disease processes. As such, UV-B and UV-C light is considered potentially harmful to healthy mammalian tissue and is considered hazardous to use. Moreover, UV is cannot be used to direct exposure for plant in case that it promotes cell and tissue death and changes the plant metabolism in unwanted and useless way. Although observations concerning light-destroying microorganisms have been reported on the effects of certain bands of UV light, the available data suggest the UV effect appears to be silent by plant cells or tissue and tissues could be damaged. Than effect of pathogen elimination from tissue can be improved with light of other wavelengths, that are more efficient for plants and moreover useful for their effective photosynthesis e.g. from the white light or visible spectrum.
Plants are vulnerable to ozone stress. Acute exposure can induce chlorosis, apoptosis and necrotic lesions, whereas accelerated leaf senescence has been observed in chronic exposure. As a mechanism for ozone-induced damages, the generation of ROS (Reactive Oxygen Species) such as superoxide and hydrogen peroxide, follow by induction of natural gaseous hormone ethylene, resulting from ozone degradation in the apoplast, has been proposed and described, though, the complete mechanism of interaction is not yet known. After penetration through the open stomata, a large part of the ozone interacts with components of the extracellular matrix. The first line of defense is the extracellular ascorbate and glutathione pool, which becomes oxidized by ozone and its reactive derivates. The antioxidant ascorbate and glutathione (reduced form) accumulates as millimolar concentrations in leaf apoplasts and may react and scavenge significant amounts of ozone derived ROS. Ascorbic acid is then recycled inside the cell in a glutathione dependent manner and transferred out through the plasma membrane to the extracellular space. The oxidation of intracellur glutathione induces the expression of several genes, some of which are associated, not only with antioxidant defense, but with abiotic stress responses and with growth and development cessation. As a result changes induced by the ozone influence the plant's metabolism as a whole
Exposure of plants to over 70 ppb of ozone results in changes in the intracellur concentration of Ca2+. This indicates oxidative activation of Ca2+ channels, similar to the response to abscisic acid-induced (ABA) increased H2O2, which causes the closure of the stomata. Oxidative activation of redox dependent Ca2+ channels, results in changes in the protein phosphorylation pattern. One of the earliest phosphorylated proteins found in experiments on rice seedlings, due to ozone fumigation, is the 66 kDa ERK-type MAPK (mitogen activated protein kinase). Ozone-induced phosphorylation stabilizes the enzyme, which in turn increases the kinase activity. Furthermore, nonenzymatic or lipoxygenase-mediated break down of lipids, ROS (in particular H2O2 as diffusible messenger), modulation of cytosolic ascorbate and glutathione relations, respectively, are well established regulatory and signalling compounds and may represent other routes of O3 triggered signalling, from the site of the chemical reaction of O3 in the apoplast or plasma membrane to the cytosol.
It is among the objects of the present invention to provide methods and apparatus that improve the resistance of plants to infection by plant pathogens, and to improve their growth characteristics by manipulation of the plant to the effects of light.